1. Technical Field
The invention relates to a position detection and positioning device that is capable of detecting and controlling very small relative displacements between two members. More particularly, the invention relates to a moving medium-type memory device that contains a controller that includes such a position detection and positioning device.
2. Description of the Prior Art
It is known to use an optical interferometer-type device or a variable capacitance-type device to detect and control very small relative displacements between two members. In the optical interferometer-type device, the range of movement can be large (for example, 1 cm or more), and the positioning accuracy can be relatively high (5 to 10 nm in a heterodyne interferometer). However, such devices require a light source, such as an He-Ne gas laser, to generate two slightly different frequencies of light, and an optical system to make these two light frequencies interfere. Accordingly, an optical interferometer-type device is large and cannot be used in the x-y stage positioning device installed on, for example, a moving medium-type memory chip.
In the variable capacitance-type device, electrodes are formed on each of the two members. Changes in the capacitance that accompany a change in the distance between the electrodes formed on one member and the electrodes formed on another member are measured, such that a very small relative displacement between the two members can be measured. In this device, as the size of the device decreases, the positioning accuracy decreases (in other words, the equipment must be made larger to increase the positioning accuracy).
An x-y stage positioning device, for example as may be installed in a moving medium-type memory chip, demands a positioning accuracy of several tens of nanometers in a range of movement of 1 mm. Increasing the size of a conventional variable capacitance-type device to improve its positioning accuracy makes such a device unsuitable for use in an x-y stage positioning device.
It would be advantageous to provide a small position detection device, especially a position detection device that can detect the relative displacement between two members with high accuracy. It would additionally be advantageous to provide a moving medium-type memory device that uses such a positioning device.